Life is so complicated! ....sorry for asking

[Voyager]

i understand halfords or the aa can check your battery's performance by attaching a reader to the terminals - my battery is under the rear passenger
seat and tricky to get to - do you know if they can take a battery performance reading from the recharge terminals that are under the bonnet and not have to access the battery directly ?

 

[nigel cross]

I doubt it as use a large resistor to load up your battery

 

[davidjpowell]

Assuming that you have a W210 E class, it is very easy to get access to the battery, even though it is under the rear seat. You might need to do it for Halfords or whoever though.

 

[grober]

You can get an indication of the battery's state of charge by simply measuring the voltage with an accurate voltmeter. Remember a fully charged "12v battery" is nominally 6x2.2 volts =13.2 V [ but even this is temperature dependent ] While this can be useful it doesn't really give a good indication of the batteries ability to produce high currents under starting conditions. For this you need a dedicated drop tester e.g Sealey Digital Battery Tester 12V : Tooled-Up.com which tests the battery under high load. Any good AUTO ELECTRICIAN could do this for you. The only problem is that this can drain the battery quite rapidly- especially if its on its last legs.